The present invention relates to a solid titanium catalyst component capable of polymerizing ethylene with high activities and preparing an ethylene polymer of excellent particle properties, and also relates to an ethylene polymerization catalyst containing the solid titanium catalyst component and an ethylene polymerization process using the catalyst.
Ethylene polymers such as homopolyethylene and linear low density polyethylene (LLDPE) have been widely used for films, because of their excellent transparency and mechanical strength.
Various processes to prepare the ethylene polymers have been conventionally proposed, and it is known that the ethylene polymers can be prepared with high polymerization activities when Ziegler catalyst comprising titanium, magnesium, halogen and optionally an electron donor is used as a polymerization catalyst. It is also known that high activities are exhibited especially when a solid titanium catalyst component obtained from a halogen-containing magnesium compound in a liquid state, a liquid titanium compound and an electron donor is used as a titanium catalyst component.
In these processes to prepare ethylene polymers, if ethylene is polymerized with much higher activities, not only the productivity is raised, but also the amount of the catalyst residue per polymer unit, particularly halogen content, is reduced, whereby a problem of mold rusting in the molding process can be solved. Therefore, development of a titanium catalyst component capable of polymerizing ethylene with much higher activities is desired.
The ethylene polymers obtained immediately after the polymerization are generally in the form of powder even if the polymerization is carried out by a slurry polymerization process or a gas phase polymerization process, and in this case it is desired that ethylene polymers having good fluidity, containing no finely divided powder and having an excellent particle size distribution are produced. The ethylene polymers showing such excellent particle properties have various advantages, for example, they can be used as they are depending on the purpose, even if they are not pelletized.
The present invention has been made under such circumstances as described above, and it is an object of the invention to provide a solid titanium catalyst component by which ethylene can be polymerized with high activities and an ethylene polymer of excellent particle properties can be prepared. It is another object of the invention to provide an ethylene polymerization catalyst containing the solid titanium catalyst component and an ethylene polymerization process using the catalyst.
A solid titanium catalyst component according to the invention is obtained by a process comprising a step of bringing (a) a liquid magnesium compound into contact with (b) a liquid titanium compound in the presence of (c) an organosilicon compound having no active hydrogen in an amount of 0.25 to 0.35 mol based on 1 mol of the magnesium compound (a) and a step of elevating the temperature of the resulting contact product (i) to a temperature of 105 to 115xc2x0 C. and maintaining the contact product (i) at this temperature, and comprises magnesium, titanium, halogen and the organosilicon compound having no active hydrogen (c).
A solid titanium catalyst component comprising those ingredients mentioned above can be obtained also by a process comprising a step of bringing (a) a liquid magnesium compound into contact with (b) a liquid titanium compound in the presence of (c) an organosilicon compound having no active hydrogen in an amount of 0.25 to 0.35 mol based on 1 mol of the magnesium compound (a) and a step of elevating the temperature of the resulting contact product (i) to maintain the contact product (i) at a given temperature of 105 to 115xc2x0 C., wherein the organosilicon compound having no active hydrogen (c) is added in an amount of not more than 0.5 mol based on 1 mol of the magnesium compound (a) while the temperature of the contact product (i) is elevated from a temperature lower by 10xc2x0 C. than the temperature maintained to a temperature at which the elevation of the temperature is completed, or after the elevation of the temperature is completed, so as to bring the compound (c) into contact with the contact product (i).
An ethylene polymerization catalyst according to the invention is formed from [I] the above-mentioned solid titanium catalyst component and [II] an organometallic compound.
In an ethylene polymerization process according to the invention, ethylene is polymerized or ethylene and a comonomer are copolymerized in the presence of the above-mentioned catalyst.